Abstract: This invention relates to bispecific antibodies having combinations of linker and hinge sequences to create linker-hinge interface domains with biological significance. Such linker-hinge interface domains covalently join two molecules, maintain the biological activities of linked molecules (target binding), stabilize the biological characteristics of new molecule (solubility and 4° C. stability), maintain the chemical, biochemical and physical properties (cytotoxicity) of the linked molecules, and modulate the biological characteristics of the linked molecules (activating T-lymphocytes without significant sign of proliferations). Both linker (GGGGS) and hinge (CPPCP) sequences are required to establish functional linker-hinge interface domains as deletion of any of the component resulted in significant lost of T-lymphocyte mediated activity.